The temperatures inside an operating gas turbine engine are extremely high, often at levels in excess of 350° C. When it is desirable to monitor the inside temperatures of components of the turbine, such as a rotating turbine blade being exposed to thousands of G's, or to monitor stresses placed upon such components during operation, a special sensing, amplifying and transmitting circuit is required. An effective solution to this problem is the use of wireless telemetry, such as that disclosed in published U.S. Patent Application Publication No US 2005/0198967 A1 entitled SMART COMPONENT FOR USE IN AN OPERATING ENVIRONMENT. In that application, the general concept of using wireless telemetry circuitry on a moving component of a gas turbine engine is disclosed. The present patent application addresses specific problems encountered when implementing a PCB for housing and supporting the wireless telemetry circuitry, which PCB must be suitable for a harsh gas turbine environment.
One exemplary prior art device is disclosed in U.S. Pat. No. 5,081,562, entitled CIRCUIT BOARD WITH HIGH HEAT DISSIPATIONS CHARACTERISTIC. This patent teaches fabrication of a circuit board having a cavity for receiving an integrated circuit device and connecting leads from circuit traces on the top rim of the cavity to connection pads on the IC. This arrangement allows the connecting leads to lie flat. However, the attachment of the device to the circuit board is also stressed significantly when the PCB is exposed to centrifugal forces in the thousands of Gs. There is no suggestion or teaching of a structure that can withstand high G-forces
Another exemplary prior art device is disclosed in U.S. Pat. No. 7,116,557 B1, entitled IMBEDDED COMPONENT INTEGRATED CIRCUIT ASSEMBLY AND METHOD OF MAKING SAME. This patent also teaches a circuit board having a cavity for receiving an integrated circuit device and connecting leads from circuit traces on the top rim of the cavity to connection pads on the IC. However, in this case the connecting leads are arched over to make an electrical connection. An encapsulating material such as silicon gel is added so as to fill the cavity and encapsulate the connecting leads. This arrangement ensures structural integrity during vibration and G-forces in the range of 10 G's but would not work in the range of thousands of G's. Moreover, the high temperature environment of a gas turbine exceeds the temperature capability of polymeric encapsulating materials, such as silicon gel or epoxy materials. High temperature capable encapsulating materials must be developed. Ceramic cements offer the potential to encapsulate electronics for high temperature use. However, the ceramic cement musty be carefully selected so as not to be electrically conductive at high temperature, particularly at radio frequencies, which would short out the radio frequency transmitter circuit.